Journal of Exposure Analysis and Environmental Epidemiology (2000) 10, 355±364 # 2000 Nature America, Inc. All rights reserved 1053-4245/00/$15.00 www.nature.com/jea Population sampling in European air pollution exposure study, EXPOLIS: comparisons between the cities and representativeness of the samples TUULIA ROTKO,a LUCY OGLESBY,b NINO KUÈ NZLIb AND MATTI J. JANTUNENc aDepartment of Environmental Hygiene, National Public Health Institute, P.O. Box 95, FIN 70701 Kuopio, Finland bUniversity of Basel, Institute of Social and Preventive Medicine, Basel, Switzerland cEU Joint Research Centre, Environment Institute, Air Quality Unit, I-21020 Ispra (VA), Italy A personal air pollution exposure study, EXPOLIS, was accomplished in six European cities among 25- to 55-year-old citizens. In order to compare the exposure results and different microenvironmental concentrations between the cities it is crucial to know the extent and effects of the population bias that has developed in sampling procedure and the sociodemographic characteristics of each measured population sample. In each participating city a random Base sample of 2000 to 3000 individuals was drawn from the census and a Short Questionnaire (SQ) was mailed to them. Two subsamples of the Respondents of the mailed questionnaire were randomly drawn: Diary sample for 48-h time±microenvironment±activity diary and extensive exposure questionnaires, and Exposure sample for the same plus personal exposure and microenvironmental monitoring. Significant differences existed between the EXPOLIS cities in the population-sampling procedure. Population-sampling bias was evaluated by comparing the Respondents with the total city populations. The share of women and individuals with more than 14 years of education is higher among the Respondents than the overall population except in Athens. Men, younger (25±34 years old) and unmarried individuals were hardest to get to participate in the study at least in Helsinki. The two subsamples differ from Respondents in having more employed and higher-educated individuals. The largest sample bias occurred at the first and easiest step of responding to the mailed Short Screening Questionnaire, and not at the last and most demanding stage of participating in the exposure measurements. Exposure data from some of EXPOLIS cities can only be compared to other cities with caution considering their large population bias or different sample selections. However the selection bias is not necessarily a problem for analyses about predictors of personal exposures or analyses within a city. Journal of Exposure Analysis and Environmental Epidemiology (2000) 10, 355±364. Keywords: demographic characteristics, European cities, personal exposure, population samples, socioeconomic factors. Introduction specific subpopulations (Jantunen et al., 1998). Six European cities: Athens, Greece; Basel, Switzerland; The goals of the EXPOLIS study (The Air Pollution Grenoble, France; Helsinki, Finland; Milan, Italy and Exposure Distributions within Adult Urban Populations in Prague, Czech Republic, were selected to represent different Europe) was to supply European air pollution exposure European regions, air-pollution situations and populations. data, which can be used to assess air-pollution distributions The most important benefit of a multicity study is to get data in populations, to search for the determinants of high from larger populations and wider variability (Katsouyanni exposures and to evaluate exposure distributions within et al., 1995). The target populations of the EXPOLIS study were the adult, urban populations of Europe. EXPOLIS focused on 1. Abbreviations: Base sample, random population sample to whom the active, working age, 25- to 55 (Grenoble 20±60) -year- SQ is sent; CO, carbon monoxide; Diary sample, subsample for TMAD and questionnaire application without exposure or microenvironmental old individuals, because their exposures are most affected monitoring ( indirect exposure assessment sample ) ; EXPOLIS,Air by urban traffic planning, zoning and occupational Pollution Exposure Distribution within Adult Urban Populations in conditions. The personalexposures and home indoor and Europe; Exposure sample, subsample for exposure and microenviron- outdoor and workplace concentrations of fine particles mental monitoring plus TMAD and questionnaire application (direct (PM2.5 ), carbon monoxide (CO) and 30 volatile organic exposure monitoring sample); PM, particulate matter; PM2.5, particles smaller than 2.5 m in aerodynamic diameter; Respondents, subjects who compounds (VOCs), together with extensive questionnaire returned a valid SQ; SQ, Short Questionnaire; TMAD, time±microenvir- and time±microenvironment±activity diary (TMAD) onment±activity diary; VOC, volatile organic compound. data were collected during 1 year from the autumn of 2. Address all correspondence to: Ms. Tuulia Rotko, Department of 1996 to the winter of 1997±1998. The overall EXPOLIS Sociology, P.O. Box 18, FIN-00014 University of Helsinki, Finland. Tel.: study design and methodology has been described in +358-9-1912-3884. Fax: +358-9-1912-3967. E-mail: [email protected] detail elsewhere (Jantunen et al., 1998; Koistinen et al., Received 20 December 1999; accepted 17 May 2000. 1999). Rotko et al. Population sampling in EXPOLIS study The goals of this paper are to present, examine, evaluate participating in exposure and microenvironmentalmonitor- and discuss the following: ing. The purpose of the Diary sample is, on one hand, to evaluate the possible changes in the time use of the o Levels and causes of population-sampling biases Exposure sample during the monitoring period and, on the introduced at each step of the population-sampling other hand, to create a larger time±microenvironment± process. activity diary database for exposure-modeling purposes. o Similarities and differences in the samples and sampling The subsample subjects were drawn randomly from the biases between the different EXPOLIS cities. Base sample database. o The sociodemographic characteristics of each participat- EXPOLIS includes a large Exposure sample (N=201) ing city, and of the various population samples within in only one city, Helsinki, where the aim was to estimate each city. both population exposure distributions and exposure o The variation from the EXPOLIS experimentaldesign as differences between different subpopulations as well as applied in each city. the relative roles of the different determinants of exposure. o The impacts of the variation of the sociodemographic In the other cities, the aim was to estimate population characteristics and experimentaldesign in each city for exposure levels and distributions for comparison between future analyses and applications of the EXPOLIS the cities and for combined analysis of the pooled data. The exposure and microenvironmentaldata. Exposure samples consisted of 50 subjects in the other cities. In addition, another 50±250 subjects, depending on sampling logistics in each city, formed the less laborious Diary samples (Table 1). In Grenoble, no separate random Base sample was formed, and the study subjects were Materials and methods volunteers. Population Sampling Short Screening Questionnaire In each city, a Base sample of 2000 to 3000 individuals was The Base samples in EXPOLIS study were contacted by a selected randomly from 25- to 55-year-old inhabitants mailed survey. The Base sample received an information (Table 1). Two subsamples of this Base sample were letter about the purpose of the EXPOLIS study and a two- drawn: subjects in subsample one (Exposure sample) to page questionnaire, which they were asked to complete and participate in exposure and microenvironmentalmonitoring send back to the local EXPOLIS center in a prepaid, and to respond to a TMAD and a generalquestionnaire, and preaddressed envelope. The purpose of the Short Screening subjects of the second subsample (Diary sample) to Questionnaire (Short Questionnaire or SQ) was to collect respond to the TMAD and the generalquestionnaire without basic background information about home and work Table 1. Number of subjects of the different population samples in EXPOLIS study. Base samplea Respondentsb Exposure samplec Diary sampled Helsinki random response rate 74% random from Respondents random from Respondents (N=2523) (N=1871) (N=201) (N=234) Athens random contacted untiltarget was random from Respondents random from Respondents (N=6968) reached (29%) (N=2000) (N=50) (N=50) Baselrandom response rate 49% random from Respondents random from Respondents (N=3000) (N=1458) (N=50) (N=282) Grenoble no base sample volunteers 20±60 years volunteers (N=54) volunteers (N=11) old half asthmatics, half controls, (N=65) Milan random response rate 25% selected, not from Base sample, random from Respondents (N=3009) (N=764) but from 15- to 55-year-old (N=250) office workers (N =50) Prague random from a limitede response rate 5% from Respondents, those from Respondents, those area in city center (N=141) willing to participate (N=50) willing to participate (N=2867) (N=36) aRandom population sample from census (Short Questionnaire mailed). bBase sample subjects who returned a valid Short Questionnaire. cExposure subsample, exposure and microenvironmental monitoring with questionnaire and time±activity data. dDiary subsample, no monitoring but questionnaire and time±activity data collected. ePrague district V. 356 Journal of Exposure Analysis and Environmental Epidemiology (2000) 10(4) Population sampling in EXPOLIS